"By itself, the figure for battery rating doesn't mean much, but seen in terms of these typical electrical loads in your car it does:"

headlights

10-15 A

parking lights

3-5 A

interior light

1-2 A

radio

1.5 A

air conditioner

15-30 A

1–200 A

The potential difference of a typical car battery is 12 V.
The potential difference is set up by the electromotive force
generated by chemical reactions. The electrolyte used in automotive
batteries is a strong solution of sulfuric acid and distilled
water. The chemical reaction inside a car battery can be reversed.
Therefore, a car battery is known as a secondary cell. A secondary
cell battery can be recharged by applying a reverse voltage.

Car batteries have three main jobs. Starting the car is most
demanding of these jobs. In order to start a car the battery must
supply 100 to 200 amps of current over a short period of time.
This can become very difficult during the winter. The chemicals
in the battery can become too cold to stir up the power necessary
to start the car motor. The second job of the car battery is to
keep itself charged by providing current for the car generator's
field. Finally, the battery of a car must supply a medium level
of current for a long period of time in order to keep the car's
electrical accessories working while the engine is not running.

There are several conventions used when measuring the current
through a battery. The Cold Cranking Amps rating (CCA) indicates
the amperes of electricity that can be delivered at 0 °F
for 30 seconds by the battery to the car. Another way the
current through a battery could be measured is the rate of discharge.
This is the ability of a battery to deliver power continuously
over a given period of time known as the discharge time. The discharge
time of most car batteries is several hours. Batteries can also be rated
in terms of useful capacity. Useful capacity is measured in ampere-hours.
A 80 amp-hour
battery will provide any combination of current and hours whose
product is 80. The useful capacity of a battery changes depending
on the discharge rate. Therefore, a battery could have a useful
capacity of 42 amp-hours at the C/10 rate of 4.2 amps, but
only 30 amp-hours at the C/1 rate of 30 A.